Hey guys....I was posting to you a while ago and my computer got a really bad virus like I never had before.
McAfee did not catch it. None of my applications open now...but I have everything backed up and to-date...I do it almost daily!
Anyway I am posting from my laptop.
All tests under room temperature, and activating the coil for 1 minute.
Used a good muti-meter AC for AC and DC for DC measurement.
Under 24VAC
Coil R80 - 140mA
Coil R12 - 310mA
Coil R5 - 490mA
Coils energized perfectly for 1 min...Non got hot except R80 got a little warm
Under 12VDC
Coil R80 - 149mA
Coil R12 - 990mA
Coil R5 - 2670mA
Coils energized until they got to hot...R80 got hotter than in AC, R12 got very hot in seconds in AC, R5 I can't get around the thick plastic encapsulation of the coil to check temp.
Very strange...R80 doesn't obey the pattern....almost same Amp draw on AC and DC (Its a small relay used mainly for handler fan motor)
Maybe its by coincidence that a coil around 80 ohms intersects, for lack of a better word, the numeric balance of both a DC and AC formula coefficients. Is the only thing I can think of!
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I will use the 12 ohm coil only for all other tests and formulas which is about the ball-park in amp draw for a contactor/coil used to turn on a residential AC Condenser (Relay controls compressor and fan)
So now, building on the same foundation analyzing one component with fixed values.
Relay designed for 24VAC with a 12 ohm coil
Again,
Under 24VAC
Coil R12 - 310mA
Energized for 1 min. - practically no noticable heat dissipation.
Under 12VDC (with a good battery, plenty of Amps)
Coil R12 - 990mA
Could not energize for more than 10-15 seconds. Coil was getting very hot.....and rising!
The amps, though, were exactly where it should be under Ohms Law 24V/12R = 1Amp (1000mA)
I wish the calculation was this easy for AC!!!
Under 12VDC tried a 180R 10W resistor to reduce the current.....coil doesn't even click.
Tried a 10R for the hack of it, to my surprise, not even with 10 ohms the coil clicks.
I like the posted circuit, safety diode, cap to take the inrush of current and 5 ohm res to limit the current.
I don't have a 5R resistor but I am afraid that if with 10R my relay didn't even click...5R will not work very well either!
I guess there is a reason why entire industry segments have their relays working on AC and not DC.